1. Field of the Invention
The field of art to which this invention pertains is thermistors and in particular to thermistor circuit arrangements which are used for the demagnetization of color television picture tubes.
2. Description of the Prior Art
Automatic demagnetization circuits are known in which a PTC-thermistor arranged in series with the demagnetization coil is used to continuously lower the magnetic field. To still further reduce the current flowing through the demagnetization coil without interrupting the heating of the PTC-thermistor, a voltage dependent resistor is connected in series with the demagnetization coil and the PTC-thermistor is supplied with the heating power additionally via a fixed resistance. It is also already known to use a PTC-thermistor heated by an alien source to reduce the demagnetization current. For this purpose the ceramic PTC-thermistor element is inserted in a tube with a heating coil applied to the exterior. A disadvantage of this measure is that the power required for the additional heating is relatively high and remains constant during the entire period during which the television receiver is on.
In addition, combinations of two thermally coupled PTC-thermistors are already known, in which case two PTC-thermistor plates are connected to one another with the aid of a heat-conducting but electrically insulating material. This PTC-thermistor combination is used to limit short circuiting currents in the heating circuit of electron tubes.
In addition, the German OS No. 2,107,365 discloses a PTC-thermistor combination which consists of two thermally close-coupled ceramic PTC-thermistor elements, in which a first PTC-thermistor element is close-coupled to a second PTC-thermistor element via the intermediary of a large-area central electrode which is highly conductive both thermally and electrically, and wherein the PTC-thermistor elements are contacted on the surfaces lying opposite the central electrode.